This invention relates to an improved process for preparing 1-organothioaldoxime compounds. More particularly, this invention is directed to a method of preparing 1-organothioaldoxime compounds by reacting an aldoxime or .alpha.-hydroxyiminoketone with an alkaline hypohalite in an acidic medium and reacting the resulting 1-haloaldoxime with the alkali metal salt of a mercaptan, said acidic medium comprising an acid added in an amount of from about 0.5 to about 4.0 equivalents for each mole of alkaline hypohalite used.
1-Organothioaldoxime compounds and their preparation by the chlorination of an aldoxime or .alpha.-hydroxyiminoketone followed by reaction with a sodium mercaptide are well known. U.S. Pat. No. 3,658,869 discloses a two-step process for preparing 1-hydrocarbylthioaldoximes in an aqueous reaction medium (essentially only water) by the halogenation of an aldoxime followed by reaction with a mercaptan in the presence of a base. The 1-hydrocarbylthioaldoximes are useful as oil additives, antioxidants, accelerators for curing rubber and as chemical intermediates. U.S. Pat. No. 3,535,361 describes a three-step process for the preparation of N-hydroxyimidothiocarboxylic acid esters which includes (1) reacting an aldehyde with a hydroxylamine in an aqueous medium to form the corresponding aldehydoxime, (2) acidifying the resulting reaction medium to a pH of at most 1 and reacting aldehydoxime with chlorine to form the corresponding chlorinated aldehydoxime and (3) reacting the chlorinated aldehydoxime with a mercapto compound to a pH of at most 1 to form the corresponding N-hydroxyimidothiocarboxylic acid ester. The N-hydroxyimidothiocarboxylic acid esters are useful as intermediates in the preparation of auxiliaries for plastics and pesticides. U.S. Pat. No. 3,778,475 relates to a process for the preparation of hydroxamoyl chlorides which includes reacting certain .alpha.-hydroxyiminoketones with elemental chlorine in an aqueous medium and under acidic conditions at a temperature of about -15.degree. to 30.degree. C. The hydroxamoyl chlorides obtained in this process are useful intermediates to thiolhydroxamate esters and carbamates having insecticidal properties. However, the main drawback of the above-mentioned prior art processes is low yield of the desired product.
U.S. Pat. No. 3,752,841 relates to the chlorination of aldoximes in a solvent containing at least 10% by weight of dimethylformamide (DMF) to form alkylhydroxamic acid chlorides which can then be converted to alkylthiohydroxamates by reaction with a mercaptan and base in the presence of the same solvent containing at least 10% by weight of dimethylformamide. The alkylthiohydroxamates can then be converted in the same solvent to alkylthiohydroxamate carbamates which are useful as insecticides. This process also suffers from a number of inherent disadvantages. The separation problems of the alkylthiohydroxamate compounds disclosed in this patent are complicated by the use of dimethylformamide since these compounds are very soluble in dimethylformamide. This makes it necessary to use costly, elaborate and cumbersome purification procedures, such as distillation, solvent extraction and the like, to isolate the final product.
U.S. Pat. No. 4,144,261 describes an improved process for preparing 1-organothioaldoxime compounds by chlorinating the corresponding aldoxime and reacting the resulting 1-haloaldoxime with the sodium salt of a mercaptan, the improvement which comprises conducting the process in an aqueous solvent containing from 5 to 75 percent by weight of a linear or cyclic polyhydric alcohol having from 2 to 20 carbon atoms. U.S. patent application Ser. No. 188,669, filed Sept. 19, 1980, discloses an improved method for preparing 1-organothioaldoxime compounds by chlorinating an .alpha.-hydroxyiminoketone and reacting the resulting 1-haloalkoxime with an alkali metal salt of a mercaptan, the improvement which comprises conducting the process in an aqueous solvent containing from about 5 to 75 percent by weight of a simple alcohol having from 1 to 4 carbon atoms or a linear or cyclic polyhydric alcohol having from 2 to 20 carbon atoms. However, neither of these two prior art references and no prior art is currently known to us which discloses, teaches or suggests the advantageous properties, i.e., enhanced yields, obtained by utilizing the claimed process of this invention.
It is desirable, therefore, and is a primary object of this invention, to provide an improved process for obtaining enhanced yields of 1-organothioaldoxime compounds by reacting an aldoxime or .alpha.-hydroxyiminoketone with an alkaline hypohalite in an acidic medium and reacting the resulting 1-haloaldoxime with the alkali metal salt of a mercaptan, said acidic medium comprising an acid added in an amount of from about 0.5 to about 4.0 equivalents for each mole of alkaline hypohalite used.
A further object of this invention is to provide additional flexibility in the choice of alternative reactants and processing conditions for the production of 1-organothioaldoxime compounds.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.